A conventional hybrid fiber-coaxial (hybrid fiber-coaxial, HFC) network provides triple-play services by incorporating an IP multimedia subsystem (IP multimedia subsystem, IMS). In this case, related data (that is, media streams) of a Voice over Internet Protocol (voice over internet protocol, VOIP) service, a video conferencing service, an Internet access service, and an interactive TV service are simultaneously transmitted over a coaxial cable. When network congestion occurs, quality of service (quality of service, QoS) guarantee is required for a communication service that has a high requirement for real-time, such as the VOIP service and the video conferencing service. According to QoS resource reservation, which is one of QoS guarantee mechanisms on the network, a calling party starts to establish a media Packet Data Protocol (packet data protocol, PDP) context on condition that QoS requirements of both parties on media streams and an encoding scheme for media streams are determined, and this process is known as the QoS resource reservation.
For the purpose of saving IP address resources and hiding a network from outside, a large number of network gateways on an existing network provide a network address translation (network address translation, NAT) function. The NAT is a standard method used to map an address domain (for example, a private Intranet) to another address domain (for example, the Internet). An IP address after NAT translation is not fixed, and is randomly assigned by a network gateway. The NAT, however, is merely characterized by address mapping on a network layer. The NAT cannot process an application-layer protocol. Therefore, how to resolve a problem of signaling/media traversal over a private network and further realize QoS guarantee for a communication service in a NAT scenario is now becoming a hot area in the field of telecommunications networks.
On a network where the HFC and IMS are integrated, the prior art, which is based on the PacketCable2.0 standard, uses a STUN server and a TURN server to interwork with a user equipment (user equipment, UE), so as to implement signal traversal and negotiation of an IP address and a port of a media proxy, thereby realizing QoS guarantee. This architecture, however, requires the user equipment to support an X2/X3 interface specially used for interworking with the STUN server and the TURN server. At present, telecommunications devices do not include the user equipment that supports the X2/X3 interface. Therefore, the foregoing solution imposes a high interface requirement on the user equipment, which is adverse to free development of the user equipment.